su.1

NAME

       su - run a shell with substitute user and group IDs

SYNOPSIS

       su  [-flmp]  [-c  command]  [-s  shell] [--login] [--fast]
       [--preserve-environment]               [--command=command]
       [--shell=shell] [-] [--help] [--version] [user [arg...]]

DESCRIPTION

       This  documentation  is no longer being maintained and may
       be inaccurate or incomplete.  The Texinfo documentation is
       now the authoritative source.

       This  manual  page  documents  the  GNU version of su.  su
       allows one user to temporarily become  another  user.   It
       runs  a  shell  with the real and effective user ID, group
       ID, and supplemental groups of USER.  If no USER is given,
       the  default  is  root,  the super-user.  The shell run is
       taken from USER's password entry, or /bin/sh  if  none  is
       specified  there.   If USER has a password, su prompts for
       the password unless run by a user with real user ID 0 (the
       super-user).

       By  default, su does not change the current directory.  It
       sets the environment variables `HOME' and `SHELL' from the
       password  entry  for  USER,  and if USER is not the super-
       user, sets `USER' and `LOGNAME' to USER.  By default,  the
       shell is not a login shell.

       If  one  or  more ARGs are given, they are passed as addi­
       tional arguments to the shell.

       su does not handle /bin/sh or other shells specially (set­
       ting  argv[0] to "-su", passing -c only to certain shells,
       etc.).

       On systems that have syslog, su can be compiled to  report
       failed,  and optionally successful, su attempts using sys­
       log.

       This  program  does  not  support  a  "wheel  group"  that
       restricts  who can su to super-user accounts, because that
       can help fascist system  administrators  hold  unwarranted
       power over other users.

   OPTIONS
       -c COMMAND, --command=COMMAND
              Pass  COMMAND, a single command line to run, to the
              shell with a  -c  option  instead  of  starting  an
              interactive shell.

       -f, --fast
              Pass  the  -f  option  to the shell.  This probably
              only makes sense with csh and tcsh, for  which  the
              -f   option   prevents  reading  the  startup  file
              (.cshrc).  With Bourne-like shells, the  -f  option
              disables filename pattern expansion, which is not a
              generally desirable thing to do.

       --help Print a usage message on standard output  and  exit
              successfully.

       -, -l, --login
              Make  the shell a login shell.  This means the fol­
              lowing.  Unset  all  environment  variables  except
              `TERM',  `HOME',  and  `SHELL'  (which  are  set as
              described above), and `USER' and  `LOGNAME'  (which
              are  set,  even  for  the  super-user, as described
              above), and set `PATH'  to  a  compiled-in  default
              value.   Change  to USER's home directory.  Prepend
              "-" to the shell's name, to make it read its  login
              startup file(s).

       -m, -p, --preserve-environment
              Do  not  change  the  environment variables `HOME',
              `USER', `LOGNAME', or `SHELL'.  Run the shell given
              in  the  environment  variable  `SHELL'  instead of
              USER's shell from /etc/passwd, unless the user run­
              ning  su  is  not the superuser and USER's shell is
              restricted.  A restricted shell is one that is  not
              listed in the file /etc/shells, or in a compiled-in
              list if that file does not exist.   Parts  of  what
              this  option  does can be overridden by --login and
              --shell.

       -s, --shell shell
              Run SHELL instead of USER's shell from /etc/passwd,
              unless the user running su is not the superuser and
              USER's shell is restricted.

       --version
              Print version information on standard  output  then
              exit successfully.

Why GNU su does not support the wheel group (by Richard Stallman)

       Sometimes a few of the users try to hold total power  over
       all  the  rest.   For example, in 1984, a few users at the
       MIT AI lab decided to seize power by changing the operator
       password  on  the Twenex system and keeping it secret from
       everyone else.  (I was able to thwart this coup  and  give
       power  back  to  the  users  by patching the kernel, but I
       wouldn't know how to do that in Unix.)

       However, occasionally the rulers do tell  someone.   Under
       the usual su mechanism, once someone learns the root pass­
       word who sympathizes with the ordinary users, he can  tell
       the  rest.   The  "wheel  group"  feature  would make this
       impossible, and thus cement the power of the rulers.
       I'm on the side of the masses, not that of the rulers.  If
       you  are  used  to  supporting the bosses and sysadmins in
       whatever they do, you might  find  this  idea  strange  at
       first.